Vertical Integration: A Confederacy of Alignment, Bonding, and Materials Technologies
- PDF / 513,406 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 46 Downloads / 183 Views
0970-Y04-05
Vertical Integration: A Confederacy of Alignment, Bonding, and Materials Technologies Shari Farrens Wafer Bonder Division, SUSS MicroTec, 228 Suss Drive, Waterbury Center, VT, 05677 ABSTRACT Vertical or 3D integration is taking hold in both the CMOS IC industry and the MEMS industry. The need for smaller devices, lower power, increased functionality, and lower cost are driving the market toward chip and wafer level stacking. Equipment suppliers have been faced with numerous challenges to meet the demands of these emerging bonding applications. This paper will discuss the confederacy of alignment, bonding and materials unions that can lead to successful outcomes in integrated manufacturing. 1. Alignment strategies for 3D integration: IR (infrared), BSA(backside alignment), and ISA (intersubstrate alignment) as they pertain to specific bond methods 2. Pros and Cons of 3D Bonding Techniques (Direct bonds, metal, adhesive, and eutectic) 3. Error analysis in alignment of 3D structures
ALIGNMENT STRATEGIES Alignment strategies build on the fundamentals from mask alignment lithography systems. Therefore it is well known that the quality of the alignment marks, separation distance (proximity versus contact), and mechanical positioning systems all contribute to final alignment accuracy. In wafer bonding the challenge is compounded by the lack of substrate transparency in most applications involving 3D integration. In order to discuss the various combinations it is first important to review the various alignment strategies. Front side marks are alignment marks that are placed on the front side or active device layer side of a substrate. These marks will become encapsulated by the bonding process and will not be visible to the naked eye after the bonding is complete. Back side marks are marks that are on the backside of the wafer and can still be viewed after bonding. These marks may or may not be removed in subsequent thinning operations. One of the earliest methods for visualizing alignment marks after bonding is to place both front side and back side marks on the substrates during fabrication. In order to achieve front side and back side marks the wafers must have lithography steps on both sides of
BSA Principle Focus on mask &
Monitor Wafer
Mask
store mask image BSA Microscopes
Load & focus on wafer
Alignment mask & microscopes move simultaneously
Figure 1: Schematic illustration of BSA (backside alignment) principles) the substrate and the quality of the backside marks are greatly enhanced when the backside of the wafer is polished. Generally backside marks are placed on the wafer during the initial lithography steps and it is not necessary to use excessive care in handling of the wafers. Figure 1 demonstrates the basic step and process flow used for backside alignment processes. This example uses a mask and a wafer. The principle is the same during wafer to wafer alignment in which the mask is replaced with a second substrate. Although the front side and back side alignment marks have been ver
Data Loading...
